The microstructure and magnetoelasticity of melt-spun Sm1 Pr Fe2 and Sm0 9Pr0 1(Fe1 B )2 alloys have been investigated using X-ray diffraction, transmission electron microscopy, three-terminal capacitance and standard strain gauge techniques. The microstructure of melt-spun Sm1 Pr Fe2 and Sm0 9Pr0 1(Fe1 B )2 is a mixture of (Sm,Pr)Fe2/(Sm,Pr)(Fe,B)2 crystalline and amorphous phases. The amount of amorphous phase with increasing Pr or B content. The microstructure of Sm0 9Pr0 1(Fe0 8B0 2)2 is almost entirely amorphous phase. The magnetostriction of melt-spun Sm1 Pr Fe2 remains almost unchanged when 0 1 but decreases with increasing x when 0 1. The magnetostriction of Sm0 9Pr0 1(Fe1 B )2 decreases with increasing y in high magnetic fields, but increases with increasing y in low fields (H 400 kA/m) due to the existence of the amorphous phase.